I'd like to provide a brief explanation to this review to put things in context: First, I'm an experienced photographer with years of practice, experimentation, and mastery (or at least attempted mastery) of various areas of photography. I know how equipment works and how to test a lens in my own home. Second, I'm not an impulsive buyer. In fact, I prefer to examine every aspect of something before hitting the buy now button. I'm sure there is a name for this condition. For these reasons, when I ordered this lens I was fully aware of both the amazing and disappointing experiences other people have had with it. However, when ordering through an Amazon (Fulfilled by Amazon) retailer I was confident that should I be able to test it properly and it appears faulty I would be able to exchange it for another copy. I had read so many positive things about this lens (the price, the sharpness wide open and the lack of coma - which is so important in astrophotography) but also some negative reviews (most common and notable the number of copies show decentering of lens elements causes uneven sharpness across frames and sloppy focus scale calibration). It was with apprehension and a nervous optimism that I opened the box when the package arrived a few days ago. There are many online resources to help you test a new lens so I won't bore you here. However, it is definitely worth noting that the sharpness/ decentration test ended up going very well. Working with such a wide-angle lens is not easy. So if you arrive through your mailbox with one of these, please note... Try twice, return once. Initially there seemed to be some decentration when viewing images of a flat wall at 100%, like any good new lens owner I went back to the tripod and tested again. It appeared that I did not have the camera aligned horizontally to the plane of the exam the first time, as corners were much sharper the second time around. Not perfect, but better. Next came the focus scale calibration test... set up on a tripod and focused (using Live View) on various objects at different distances on the scale. Surprisingly very accurate at short and medium ranges - a nice surprise given some of the reviews I read. Next came the most important test for astrophotography... infinity focus. A lot of the bad reviews I read stated that the infinity focus was way off the mark on the lens focusing scale. So I focused on a distant tree using Live View. Hmmm, at first I was worried that my new lens, which has been good so far, wasn't quite focused at infinity. In fact, it felt like true infinity was occurring AFTER the focus stop (contrary to the reviews I'd read which suggests some copies were focused in an infinity way before the infinity mark on the lens) A 100% review on the monitor was inconclusive. This left me with only one option - go shoot some stars. Well, to cut a long story short, the day after this lens arrived I found myself on a hilltop in the black of night with my tripod, new lens and shutter button... Heaven! Using Live View (and the appropriate camera settings), I focused on a bright star next to the Milky Way (reaching just a little past the infinity mark on the focus dial), released the shutter, zoomed in on the image on the back of my camera, and was blown away. When I got home and looked at the image at 100%, I could see some slight decentrations in two extreme corners at 100%, but nothing to worry about at all. The importance of the lens's ability to focus on infinity (the stars) had been proven. It's sharp and wide enough to capture a large portion of the Milky Way. In short, this lens is not perfect. But it's easily good enough to become a long-term keeper for me. I've tested it and I know it will take the pictures I want it to take. It has my trust. If you are like me and have read all the reviews and done all the research (and are reading this review now to try and help you make a decision), just go for it. My guess is that K&F Concept acted on the feedback regarding the Infinity focus and implemented a process in their quality control workflow to ensure they ship with accurate focus scales.